Cannot start qt application with gtk2 theme

[fcole90]

Trying to run apps with qt gtk2 theme makes the app crash.

# Logs:
(python3.8:471377): GLib-GObject-WARNING **: 18:01:22.268: cannot register existing type 'GdkDisplayManager'

(python3.8:471377): GLib-CRITICAL **: 18:01:22.268: g_once_init_leave: assertion 'result != 0' failed

(python3.8:471377): GLib-GObject-CRITICAL **: 18:01:22.268: g_object_new_with_properties: assertion 'G_TYPE_IS_OBJECT (object_type)' failed

(python3.8:471377): GLib-GObject-WARNING **: 18:01:22.268: invalid (NULL) pointer instance

(python3.8:471377): GLib-GObject-CRITICAL **: 18:01:22.268: g_signal_connect_data: assertion 'G_TYPE_CHECK_INSTANCE (instance)' failed

(python3.8:471377): GLib-GObject-WARNING **: 18:01:22.268: invalid (NULL) pointer instance

(python3.8:471377): GLib-GObject-CRITICAL **: 18:01:22.268: g_signal_connect_data: assertion 'G_TYPE_CHECK_INSTANCE (instance)' failed

(python3.8:471377): GLib-GObject-WARNING **: 18:01:22.268: cannot register existing type 'GdkDisplay'

(python3.8:471377): GLib-CRITICAL **: 18:01:22.268: g_once_init_leave: assertion 'result != 0' failed

(python3.8:471377): GLib-GObject-CRITICAL **: 18:01:22.268: g_type_register_static: assertion 'parent_type > 0' failed

(python3.8:471377): GLib-CRITICAL **: 18:01:22.268: g_once_init_leave: assertion 'result != 0' failed

(python3.8:471377): GLib-GObject-CRITICAL **: 18:01:22.268: g_object_new_with_properties: assertion 'G_TYPE_IS_OBJECT (object_type)' failed

Process finished with exit code 139 (interrupted by signal 11: SIGSEGV)

# Symple application failing
import sys
from PySide2.QtWidgets import QApplication, QDialog, QLineEdit, QPushButton

class Form(QDialog):

    def __init__(self, parent=None):
        super(Form, self).__init__(parent)
        self.setWindowTitle("My Form")

if __name__ == '__main__':
    # Create the Qt Application
    app = QApplication(sys.argv)
    app.setStyle('gtk2')
    # Create and show the form
    form = Form()
    form.show()
    # Run the main Qt loop
    sys.exit(app.exec_())

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: qt5-gtk2-platformtheme 5.0.0+git23.g335dbec-3ubuntu4
ProcVersionSignature: Ubuntu 5.4.0-24.28-generic 5.4.30
Uname: Linux 5.4.0-24-generic x86_64
ApportVersion: 2.20.11-0ubuntu27
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: GNOME
Date: Tue Apr 21 17:57:21 2020
InstallationDate: Installed on 2020-04-03 (17 days ago)
InstallationMedia: Ubuntu 20.04 LTS "Focal Fossa" - Beta amd64 (20200401)
SourcePackage: qtstyleplugins-src
UpgradeStatus: No upgrade log present (probably fresh install)

[fcole90 (fcole90)]

Checking further logs I get the following:

python3.8[471723]: segfault at 114 ip 00007f0439c6caa5 sp 00007fff05b55770 error 6 in libgdk-x11-2.0.so.0.2400.32[7f0439c36000+5e000]

Code: 64 24 10 4c 8d 6c 24 40 e8 d8 fe ff ff 31 f6 48 8d 5c 24 38 48 89 c7 31 c0 e8 77 c9 fc ff 31 d2 48 8d 35 0e fe ff ff 48 89 ef <c7> 80 14 01 00 00 01 00 00 00 49 89 c7 48 89 a8 d8 00 00 00 e8 12

[fcole90 (fcole90)]

You need the following packages to run the script:
sudo apt install libpyside2-py3-5.14 python3-pyside2.qtcore python3-pyside2.qtuitools python3-pyside2.qtwidgets qt5-style-plugins qt5-gtk2-platformtheme

[Dmitry Shachnev (mitya57)]

Make sure you set QT_QPA_PLATFORMTHEME=gtk2 environment variable, like the package description says.

[fcole90 (fcole90)]

You are right, it works correctly doing so. It can be closed. Thanks for your quick reply.